The present invention relates to formulations for lipid vesicles and methods of their manufacture. More particularly, the present invention discloses paucilamellar lipid vesicles designed of materials which have exceptional properties for cosmetic, edible, dermatological, and pharmaceutical use.
Lipid vesicles are substantially spherical structures made of amphiphiles, e.g., surfactants or phospholipids. The lipids of these spherical vesicles are generally organized in the form of lipid bilayers, e.g., multiple onion-like shells of lipid bilayers which encompass an aqueous volume between the bilayers. Paucilamellar lipid vesicles have 2-10 peripheral bilayers which surround a large, unstructured central cavity.
Until recently, liposome technology has been concerned mostly with vesicles composed of phospholipids. This is primarily because phospholipids are the principal structural components of natural membranes and, accordingly, lipid vesicles have been used as a model system for studying natural membranes. However, there are a number of problems associated with using phospholipids as synthetic membranes. Biological membranes are stabilized by membrane proteins and maintained by extensive enzymatic "support" systems that rapidly turn over, exchange or modify membrane lipids. Neither membrane proteins nor the requisite enzymatic support systems can be practically incorporated into the wall structure of liposomes, making the structures inherently less stable than natural membranes. In addition, the biological environment contains several potent phospholipases that rapidly break down free phospholipids. These phospholipids will attack liposomes and degrade the membrane. For these reasons, phospholipid liposomes are rapidly degraded in vivo.
Moreover, phospholipid liposome technology has other problems. Phospholipids are labile and expensive to purify or synthesize. In addition, classic phospholipid liposomes are in the form of multilamellar as opposed to paucilamellar vesicles and have poor carrying capacities, especially for lipophilic materials, and have poor shelf lives unless lyophilized in the dark with antioxidants. Finally, phospholipids degrade too rapidly in vivo for most pharmaceutical or vaccine applications. For these reasons, there is increasing interest in the art for paucilamellar lipid vesicles made of other amphiphilic compounds.